Aircraft fuel monitor

ABSTRACT

A system utilizing a two-circuit vacuum switch to monitor suction in the fuel system between the fuel selector valve and the engine-driven pump and warn the pilot of a restriction in the system or that the fuel tank from which the engine is feeding is exhausted of fuel.

BRIEF SUMMARY

[0001] The object of the invention is to provide pilots of low-wing, multi-fuel-tank aircraft with a warning that they are about to experience engine failure due to fuel starvation 1) because of a blockage or restriction in the system, usually caused by improper fuel selector position or a clogged fuel tank vent, or 2) because the fuel tank in use is exhausted of fuel. The invention provides a warning via lights on the instrument panel in sufficient time to allow the pilot to take corrective action before the engine quits. The system is low-cost and easy to install.

BRIEF DESCRIPTION OF DRAWINGS

[0002]FIG. 1: Instrument panel warning light array

[0003]1) 3-way switch

[0004]2) Daylight fuel restriction warning light

[0005]3) Tank empty daylight warning light

[0006]4) Night restriction warning light

[0007]5) Tank empty night warning light

[0008] Note: 2) and 3) are bright red lights for daytime use.

[0009]4) and 5) are smaller, much dimmer lights so as not to impair a pilot's vision should he get a warning light at a critical time at night.

[0010]FIG. 2: A schematic of a fuel system incorporating present invention

[0011]1), 2) Left and right fuel tanks

[0012]3) Fuel selector valve

[0013]4) Engine-driven fuel pump

[0014]5) “T” fitting on outlet side of selector valve

[0015]6) Two-circuit vacuum switch

[0016]7) Instrument panel warning light array

DETAILED DESCRIPTION

[0017] This simple but effective warning system monitors the suction in the fuel system between the fuel selector valve and the engine-driven fuel pump. The main component of the system is a commercially available two-circuit stainless steel diaphragm vacuum switch containing two adjustable snap-action switches. A “T” fitting is installed at the outlet port on the selector valve and a tube is installed between that point and the vacuum switch.

[0018] One circuit of the vacuum switch is normally open and is set to activate at a pressure slightly above the negative pressure generated in the fuel system at takeoff power. Any obstruction in the system, such as the selector valve being in the off position or in any position except in a detent for a fuel tank, will result in increased suction in the system, activating that switch and giving the pilot an immediate warning. A plugged fuel tank air vent also will result in increased suction, activating that switch and warning the pilot to check his selector valve and/or switch fuel tanks.

[0019] The second circuit is normally closed and is set to activate at a pressure slightly below the suction existing in the system at cruise power. Its purpose is to alert the pilot that the tank the engine is feeding from is exhausted of fuel. When air in the empty tank reaches the sensor tube for the vacuum switch, the lower suction activates the switch. This usually begins with air bubbles causing intermittent activation.

[0020] The vacuum switches activate warning lights on the instrument panel, one labeled “FUEL RESTRICTED” and the other “TANK EMPTY.” If the pilot gets a warning light and corrects the problem in a timely fashion, the engine will not suffer a loss of power. An aural warning can be incorporated into the system that will activate if either warning light comes on. 

What is claimed
 1. A system that will warn a pilot of a low-wing, multi-fuel-tank aircraft of a restriction in the fuel system and warn of an exhausted fuel tank by monitoring the suction in the fuel system between the fuel tank selector and the engine-driven pump. 